Highly selective thioalcohol modified phthalocyanine sensors for Ag(i) and Pd(ii) based on target induced J- and H-type aggregations: synthesis, electrochemistry and peripheral metal ion binding studies

Abstract

We have described highly selective 1(4),8(11),15(18),22(25)-(1-hydroxyhexan-3-ylthio)-phthalocyanine sensors, M{Pc[α-SCH(C₃H₇)(C₂H₅OH)]₄} (MPc(α-HHT)₄, where M = Zn(II) (2), Cu(II ) (3) or Co(II ) (4) and HHT: –SCH(C₃H₇)(C₂H₅OH)). The formation of S–M–S {S = sulfur; M = Ag(I) or Pd(II)} bonds on the periphery in the case of Ag(I) and Pd(II) metal ions induces H- or J-aggregation, respectively, which results in significant changes in the absorption of the B- and, in particular, the Q-band. The binding ratios of Ag(I) to the periphery of 2 and 3 were found to be ca. 2 : 1 and 3 : 2, respectively. On the other hand, the binding ratios of Pd(II) to the periphery of the same compounds were found to be 3 : 1 and 4 : 1. The fluorescence of 2 exhibited distinct changes in response to treatment with Ag(I) and Pd(II) ions in solution. The fluorescence spectra emission intensity of 2 was quenched upon titration with Ag(I) and Pd(II) and a new emission maximum was observed upon titration with Pd(II). FTIR, ¹H-NMR, ¹³C-NMR, UV–vis, MALDI-TOF MS and elemental analysis data were used to characterize the novel compounds. Transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FE-SEM) were also used as complementary techniques to investigate the morphology and to image the interfacial aggregates of 2. The redox behaviours of the complexes were examined by voltammetry and in situ spectroelectrochemistry on Pt in a nonaqueous medium.